Much work has been done over the years on processes for obtaining liquid products from solid carbonaceous materials such as coal. Coal liquefaction is such a process and is primarily a thermal process wherein retrogressive reactions occur in the early stages that have an adverse effect of efficiency. It has been found that such retrogressive reactions can be reduced by use of various catalysts, such as transition metal sulfides. Various metal catalyst precursors have been used which decompose at elevated temperatures and react with sulfur-containing compounds to form the corresponding metal sulfides. Typical catalyst precursors include inorganic salts and heteropoly acids, such as phosphomolybdic acid. These catalyst precursors, which are usually in the form of an aqueous solution are introduced into the coal by conventional techniques, such as by impregnation or by blending it into a recycle stream. Either way, drying and activation steps must be employed.
Another type of precursor is the oil soluble type which has the advantage of direct addition into the coal slurry. The primary disadvantage of conventional oil soluble precursors are their relatively high costs and low metals content.
Consequently, there still exists a need in the art for improved coal liquefaction processes which have the advantage of oil soluble catalyst precursors, but without their disadvantages.